In a manufacturing facility, liquid chemicals are frequently used in various manufacturing processes. For instance, in a semiconductor fabrication plant, a semi-conducting substrate must be processed in a multiplicity of manufacturing steps, i.e., as many as several hundred, in order to make an integrated circuit chip. The multiplicity of manufacturing steps may include etching, cleaning, deposition or any other necessary processing steps. A variety of chemicals, including liquids and gases must be used in these steps. For instance, to etch a specific feature on a substrate, to clean after each etching or deposition steps, to deposit layers of materials on the substrate, or to carry out any other necessary processing procedures.
The variety of chemicals used in a semiconductor fabrication plant must be handled with extreme care since most of those processing liquids are either highly toxic and/or highly corrosive. For instance, strong acids are frequently used in an etcher for etching a specific structure on a semiconductor wafer. Since the acid material is not normally all consumed in the etching process, unused acid must be recycled or otherwise disposed. Due to their corrosive and toxic nature, the acid must be carefully handled and transported to avoid personal injuries and potential fire hazard.
A conventional chemical collection system 10 is shown in FIG. 1. The system 10 consists mainly of a first collection tank 12 (or a buffer tank), a second collection tank 16 and a manually operated valve 18. The first tank 12 has a waste chemical inlet 20 for the intake of waste liquid chemicals from a process machine. When the process machine is an etcher, the waste chemical is most likely a waste acid from an etching process.
As shown in FIG. 1, the first tank 12 is provided with three liquid level detectors, i.e., a low level detector 22, a mid-level detector 24, and a high level detector 26. The level detectors may be constructed of a resistance type or any other suitable type that will trigger a warning system 28. The warning system 28 may have several warning lights or alarms each corresponds to the low, mid- or high level detector 22, 24 and 26. Depending on the operating procedure at a fabrication plant, a machine operator must manually open valve 18 when the liquid level 30 in the first tank 12 reaches the low level detector 22, the mid-level detector 24 or the high level detector 26. Most manufacturing plants are provided with a warning system such that the low level detector is used as an indicator for the operator to open valve 18, while the mid- and high level detectors are used as additional safety devices to further warn the machine operator to open valve 18. When valve 18 is fully opened, the waste chemical 32 in the first collection tank 12 is drained to the second collection tank 16. The liquid level 34 in the second tank 16 must be carefully monitored so that the waste chemical 32 does not overflow from the tank. Any accidental overflow can cause injury to plant personnel and furthermore, fire hazard or property damage.
The conventional system shown in FIG. 1 has several drawbacks when it is in operation. First, the warning signals 28 may not give adequate warning to a machine operator to manually open valve 18 in order to drain the waste chemical contained in the first tank 12. Secondly, when the liquid level 34 in the second collection tank 16 is not carefully monitored, the accidental overflow of a waste chemical from the second tank can cause severe problems in a fabrication plant. The placement of the second collection tank 16 in a semiconductor fabrication plant causes additional problems since it is frequently placed at a location that is one or two floor levels below the first tank 12, while the first tank 12 is frequently placed at or near a process machine such as an etcher. When the second collection tank 16 is placed one or two floors away from the process machine, the machine operator frequently forgets to monitor the fluid level 34 in the second tank 16. Problems are frequently caused by such negligence which leads to personnel injuries or facility damages. Furthermore, when the machine operator forgets to open valve 18 to drain waste chemical 32 from the first tank 12, the first tank 12 may overflow such that the process machine must be shut down.
It is therefore an object of the present invention to provide a chemical drain system that does not have the drawbacks or shortcomings of the conventional chemical drain systems.
It is another object of the present invention to provide a chemical drain system that consists of two waste chemical collection tanks and a microprocessor controlled valve thereinbetween.
It is a further object of the present invention to provide a chemical drain system that consists of a first collection tank, a second collection tank and a microprocessor controlled valve thereinbeteween for draining from the first tank to the second tank when a level sensor in the first tank detects a certain liquid level is reached.
It is still another object of the present invention to provide a chemical drain system that consists of two collection tanks, a computer controlled valve thereinbetween, and an electronic scale for the second tank such that the valve is automatically shut when a full second collection tank is detected.
It is yet another object of the present invention to provide a chemical drain system that consists of two collection tanks, a computer controlled valve thereinbetween, a microprocessor controller and an electronic scale capable of sending a signal to the controller when a full second collection tank is detected.
It is another further object of the present invention to provide an automated chemical drain system that consists of two collection tanks and a computer controlled valve thereinbetween wherein the first tank is equipped with at least two level sensors for detecting the liquid level in the tank.